The present invention relates to the field of power supplies and, more particularly, to step-down DC-DC converters or step-down switching regulators wherein controlling the main and auxiliary output voltages is desired.
Switching regulators, including ripple regulators, are commonly used because of their characteristic of high efficiency and high power density (i.e., power-to-volume ratio) resulting from smaller magnetic, capacitive, and heat sink components. Switching regulators indirectly regulate an average DC output voltage by selectively storing energy by switching energy on and off an inductor. By comparing the output voltage to a reference voltage, the inductor current is controlled to provide the desired output voltage.
Synchronous buck power stages are a specific type of switching regulator that use two power switches such as power MOSFET transistors to control current in the output inductor. A high-side switch selectively couples the inductor to a positive power supply while a low-side switch selectively couples the inductor to ground. A control processor typically referred to as a pulse width modulation (PWM) is used to control the high-side and low-side switches. Synchronous buck regulators provide high efficiency when low on-resistance power MOSFET devices are used.
For DC-DC converters, there is a need for a converter that can provide an auxiliary regulated voltage in addition to the main output voltage. It is desirable to synchronize these two main and auxiliary converters as well as track the main and auxiliary voltages. The prior art typically has utilized independent controllers to control the main DC-DC converter and the auxiliary DC-DC converter.
The present invention provides a circuit that controls an auxiliary voltage with the help of the main controller. This circuit provides switching synchronization, which is inherent in the topology, as well as tracking the auxiliary voltage with the main output voltage, desirable in many applications. Synchronization is achieved by turning on the upper switches at the same time, with the use of an edge trigger. Tracking is achieved by referencing the auxiliary output to the main output.